1. Field of the Invention
The present invention relates to a V-shaped engine, and more particularly a V-shaped engine including a mechanism that reduces vibration caused by a secondary component of an inertia couple caused by lateral pressures from pistons.
2. Description of the Related Art
Engines include reciprocating engines, for example. A reciprocating engine includes a motion conversion mechanism for converting reciprocating movements of the piston into rotational movements of the crankshaft (hereinafter referred to as piston-crank mechanism).
As the piston-crank mechanism operates, vibration occurs. In view of this, in a reciprocating engine, a mechanism is provided for reducing vibration generated as the piston-crank mechanism operates (hereinafter referred to as balancer mechanism).
Some reciprocating engines include a plurality of cylinders (such an engine will be hereinafter referred to as multi-cylinder engine). Some multi-cylinder engines have two cylinders positioned next to each other around the axis of the crankshaft as viewed in the axial direction of the crankshaft, where one of the cylinders is angled relative to the other one (such an engine will be hereinafter referred to as V-shaped engine).
In a two-cylinder V-shaped engine, the angle of one cylinder relative to the other (hereinafter referred to as a bank angle) may be 90° such that vibration caused by a primary component of an inertia force generated as the piston-crank mechanism operates (hereinafter referred to as primary inertia force) can be cancelled out. Further, if the crankpin rotatably supporting the connecting rod connected to the piston in one cylinder and the crankpin rotatably supporting the connecting rod connected to the piston in the other cylinder are arranged around the shaft center of the crankshaft with a predetermined phase difference, i.e., the engine has a phase crank, it is possible to cancel out the primary component of the inertia force generated as the piston-crank mechanism operates even if the bank angle is not 90°.
In a two-cylinder V-shaped engine, a balancer mechanism is provided to reduce vibration caused by a secondary component of an inertia force generated as the piston-crank mechanism operates (hereinafter referred to as a secondary inertia force). The balancer mechanism is disclosed, for example, in Japanese Patent No. 4430462.
A secondary inertia force generated as the piston-crank mechanism operates includes, in addition to a secondary component of an inertia force produced by the reciprocating motion mass of the piston-crank mechanism (hereinafter referred to as secondary inertia force), a secondary component of an inertia couple caused by lateral pressures from the pistons (hereinafter referred to as secondary inertia couple). The secondary inertia couple caused by the lateral pressures from the pistons may cause vibration. Accordingly, it is preferable to reduce vibration generated by the secondary inertia couple caused by the lateral pressures from the pistons, as well. The invention disclosed in Japanese Patent No. 4430462 does not consider how to reduce vibration generated by the secondary inertia couple caused by the lateral pressures from the pistons.